The invention relates to a method for determining the ignition angle for an internal combustion engine with adaptive knocking control.
German patent document DE 40 08 170 A1, for example, discloses such an adaptive knocking control of an internal combustion engine, in which the ignition angle is read out from a characteristic diagram, and is by a predetermined amount when knocking occurs. The ignition angle is then advanced by a reduced amount until knocking again occurs. When the engine leaves a predetermined operating range, the current ignition angle is stored in an adaptive characteristic diagram for reuse the next time the operating range is reached. DE 40 01 476 A1 discloses how, instead of the current ignition angle, the mean value of the control ranges in the operating range are stored in the adaptive characteristic diagram.
The tendency of an internal combustion engine to knock increases as the rotational speed rises and the fuel quality (the so-called RON value) decreases. The dependence of the rotational speed is taken into account, for example, according to DE 42 05 889 A1, via a rotational speed-dependent weighting factor for the control range of the knocking control. In addition, in order to take into account the RON value of the fuel used, it is known to use different characteristic diagrams for the set point ignition angle. The changeover between these characteristic diagrams is carried out via a mechanical or electronic switch which has to be activated manually when the user of the vehicle fills the vehicle fuel tank with fuel of a different quality. If this changeover process is forgotten, or not carried out for some other reasons, knocking increases. Additionally, with these methods, the influence of the ambient air pressure on the occurrence of knocking events is not taken into account.
The object of the invention is to provide a method and apparatus for adaptive knocking control for internal combustion engines which automatically takes into account the effects of ambient conditions and the fuel quality.
This and other objects and advantages are achieved by the method and apparatus according to the invention, in which the occurrence of knocking is reduced by a controlled adjustment of the ignition angle in the retarded direction. The current values for the adjustment in the retarded direction are stored in a characteristic diagram in an operating parameter-dependent fashion. An average adjustment in the retarded direction is determined from these characteristic diagram values, and both a correction ignition angle and a control range limitation for the knocking control are determined therefrom. The fuel quality and ambient influences are automatically sensed with reference to a learned RON level, and are also used to reduce the amount of energy expended to control engine knocking.
In this manner, it is simple and easy to take into account the fuel quality and ambient influences on the knocking control of an internal combustion engine. On the one hand, the expected fuel quality and ambient conditions can be predefined by means of a starting value. On the other hand, however, deviations from these are taken into account by determining a learned RON level from the average retarded-direction adjustment angles.
The knocking control can be relieved of work by predefining a correction ignition angle on the basis of the current RON level. At the same time, by predefining the maximum control range as a function of the learned RON level, the sum of the correction ignition angle and the actual ignition angle adjustment of the knocking control is prevented from exceeding the permissible range.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.